Is Cystic Fibrosis Genetic Testing Accurate And Other FAQs

What is Cystic Fibrosis?

Cystic Fibrosis (CF) is a rare genetic disease that is life-threatening. It affects approximately 75,000 people in North America, Europe, and Australia.A total of 200,000 people are affected in the US with an approximate 1000 new cases per year. Americans of Caucasian origin are most likely to be diagnosed with cystic fibrosis. Currently, nearly three-quarters of all cystic fibrosis cases are diagnosed by the age of two. Despite the many biotechnological advancements that have been made, the life expectancy of the disease is still around 40. It is a breathing disorder that affects the lungs. People who have it have a difficult time breathing properly. The best way to describe it is to imagine you are deep below the surface of the ocean. All that water above you is weighing down on you, making it impossible to breathe. You are struggling for air and the only way to breathe in some air is through a narrow straw that connects you to the area above the surface of the water. So, you carefully breathe in air in such a way that the straw doesn’t collapse. Imagine this type of breathing all your life—that is CF. This sounds frightening.

What is Cystic Fibrosis Genetics?

Mutations in the CFTR gene cause relevant proteins to break down and malfunction. This affects the cells that produce mucus, sweat, and digestive juices.

In healthy people, these juices are thin and slippery. In individuals with CF, these liquids are the opposite: sticky and think. And, rather than acting as a lubricant which helps the lungs breathe smoothly, the secretions clog tubes, ducts, and passageways. This is a particularly sticky situation in the lungs and pancreas.

This then causes a buildup of thick mucus around the lungs which causes lung dehydration and essentially makes breathing very difficult and almost impossible. In other words, the lungs cannot clear themselves. Cystic fibrosis is considered to be an autosomal recessive disorder. A mouthful, I know. That essentially means that someone who has the disease has two copies of the mutation in the CFTR gene from a carrier, say one from dad and one from mom has the disease. Though connected to family historythis is only the case if someone has two copies of the gene. This is different from so-called carriers of the mutation who only have one copy and no symptoms. An estimated 10 million Americans are a CF carrier of the mutation. This is scary if you think about it. The chances of any male and female CF carrier among the 10 million meeting and having a child are quite high. There are nearly 2,000 mutations related to cystic fibrosis, some of which can be detected via genetic screening.

Is Cystic Fibrosis Genetic Testing Accurate?

Is Cystic Fibrosis Genetic Testing Accurate

Yes, and no. Out of the 2,000 cystic fibrosis mutations that have been found, during a genetic test less than 300 are genetically testable, so to say. This has been helpful. Thanks to genetic test advancements, the life expectancy of those with cystic fibrosis has increased by ten years—from 27 to 37. These advancements have also helped doctors figure out not only which patients have cystic fibrosis, but also which ones are at risk and which drugs or medications are best suited for them. This is especially helpful for parents who wish to have a baby; genetic testing may help them figure out what the chances are their baby will have the disease. These have all greatly advanced the area of genetic testing for cystic fibrosis. However, screening of only 300 genes is not enough. This leaves the other 1,700 or so in the dark in terms of screening, but they could be important in predicting disease status. So, yes, the tests that are designed to test the less than 300 genes for cystic fibrosis are accurate, but are they enough to predict all the cases of cystic fibrosis given that there are 2,000 mutations for it? Probably not. That is why genetic screening is not considered a gold standard when it comes to diagnosing cystic fibrosis.

How Is Cystic Fibrosis Diagnosed?

Cystic fibrosis is currently diagnosed through a chloride sweat test. The science world refers to it as pilocarpine iontophoresis, but let’s just call it the sweat test for our purposes. During the sweat test, the patient takes a chemical activator (pilocarpine), which causes them to secrete chloride on their skin. The sweat test, as its name implies, measures the concentration of chloride, or essentially salt, in the patient’s sweat. This technique has been around for decades. Even though it is old, its accuracy rate is around 98%. And while it is accurate, it doesn’t provide any information other than a positive or negative result. In other words, patients and doctors can only get a yes or no answer. It offers no information about the severity of symptoms or which therapies might be most effective or suitable. This is a big deal since the severity of the disease varies greatly among patients.

What Is the Future of Cystic Fibrosis?

Despite the fact that cystic fibrosis diagnostics are not optimal, we have to look at things from the bright side and not sweat the small stuff. Great advancements have been made, indeed. This includes advances in both technology as well as treatment. Thanks to that, children with the disease are living into adulthood. In fact, over 50% of the patients with the disease are older than 18. Their median predicted survival age (meaning the most frequent survival age among the cystic fibrosis group) is constantly on the rise and is now close to 40. So, overall, perhaps rather than asking whether genetic testing for cystic fibrosis is accurate, we should be asking if it is better than before, which it definitely is. Given that the numbers have improved rapidly over the past few years, it is not unrealistic to expect more and more rapid advancements in the coming years.

Laura Day
 

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